HADCRUT Update August 2012
By Paul Homewood
Just a quick update of the August Global Temperature figures. HADCRUT3V numbers finally came in for the month last week while I was away, so the chart looks like this.
|August 2012 anomaly||0.26||0.34||0.51||0.56|
|Inc/Dec from last month||-0.03||+0.06||+0.06||+0.09|
|12 month running average||0.16||0.18||0.36||0.50|
The 12 month average for HADCRUT remains at 0.36C, the same as in July. A look at the long term shows a similar picture to the other three datasets, with current temperatures running below those from 2002-2007. Remember that the detail on the other datasets is already posted here.
With the HADCRUT figures in, as promised, I can now show how temperatures trends have diverged since satellite monitoring began in 1979. Each of the four datasets uses a different baseline for calculation of anomalies (detail here), so naturally the numbers are all different. In order to compare them directly, I have re-centred GISS, HADCRUT and UAH to the anomalies that RSS show for 1979. For example:-
RSS – 1979 : -0.09C
GISS – 1979: +0.10C
GISS Re-centred 1979: +0.10 – 0.19C = –0.09
Therefore all GISS anomalies are reduced by 0.19C. Note that this does not affect the GISS trend at all, but simply shifts the scale on the graph. When all the datasets are re-centred in this way, the trends since 1979 look like this.
Based on 12 month running averages and with all four sets starting at the same point, GISS clearly come up with a significantly greater warming trend than the other sets. Furthermore, this divergence has really only taken off since around 2001. Until then there were occasional fluctuations, but the GISS figures tended to fit into the overall pattern of things. The actual numbers illustrate just how big the divergence has been.
|12-Month Running Average||Increase 1979-2012|
In other words, more than a third of the warming that GISS claim is not shown by RSS. It is also worth pointing out here that UAH are in the middle of introducing their new Version 5.5. More on this next month, but in simple terms they have been picking up spurious warming because of problems with the Aqua system. The new Version, which I will be using in my next update, effectively reduces temperatures for the last year by about 0.05C. This will bring UAH closely into line with RSS and HADCRUT, and emphatically leaves GISS as an outlier.
Something else worth pointing out is that RSS have less coverage of the Antarctic than UAH. RSS can only monitor down to 70oS, whereas UAH go to 85oS. Why is this significant? It is generally accepted that the Antarctic has been getting colder in recent years. It seems unlikely that RSS are picking up the full effect of this in their global numbers, which, if that were the case, would be over estimated.
More on this and a closer look at the trends over the last decade in the September update. Hopefully the HADCRUT figures will be on time for this!